1. Field of the Invention
The present invention relates to a projection image display apparatus for performing an image display through projecting an enlarged image of color onto a screen, for example. And, in particular, the present invention relates to a projection image display apparatus for obtaining the enlarged image on the screen by projecting it obliquely onto the screen, and also a projection optical unit to be used therein.
2. Description of the Related Art
For so-called a projection-type color image display apparatus, for projecting a color picture on an image display element, such as, a projection-type cathode ray tube (CRT) or a liquid crystal display apparatus (i.e., a liquid crystal panel), etc., for example, enlargedly, on a screen through a projection optical system, requirement is made on reduction in the size, in particular, the depth of the apparatus, as well as, obtaining an enlarged image of sufficient large sizes on the screen. For achieving such the requirement, conventionally, as is described in Japanese Patent Laying-Open No. Hei 5-134213 (1993) <Patent Document 1>, Japanese Patent Laying-Open No. 2000-162344 (2000) <Patent Document 2> and Japanese Patent Laying-Open No. 2002-357768 (2002) <Patent Document 3>, for example, there is already known a technology of enlarging and projecting the image onto the screen from a direction oblique or inclined thereto (by a predetermined angle with respect to a normal line on the screen).